How long have you owned this X5?

The low antifreeze is probably normal and nothing to be concerned about. If it really gets low you'll get a warning on the dash.

The "won't heat properly" could just be your vent settings - might have cool air being directed to the dash vents and warm air to the feet, for example, which could cause someone to conclude it isn't putting out heat. Easy enough to check settings in iDrive.

The oil could be the compressor. I've never had one go bad, but I hear others have. I trust my indy, so if he told me that I'd probably let him do the work. But I might get the car good and warmed up, then turn the AC on full blast and full cold setting to see if it works. If it doesn't put out some cold (and I see you're in WI and winter is two weeks away), then something is wrong. If you don't trust your indy, ask around at the BMW club for a new shop.

__________________
Mike

2005 e53 X5 4.8is 169k miles
2018 f90 M5
2018 Volvo XC60